Locking bar for screen-printing frame

ABSTRACT

A screen-printing frame having a screen-tensioning arrangement including a frame supporting a channel member which receives a locking bar. The screen material is positioned over the channel and the locking bar inserted to force the screen into the channel where it is positively gripped. Means is provided to move the channel relative to the frame to provide for tensioning after the screen is securely gripped. The tension on the screen serves to move the locking bar into tighter engagement with the channel, thus increasing the grip on the screen. Resilient means is provided in the bottom of the channel to maintain the screen material in engagement with the locking bar during initial insertion and rotation of the bar to the locked position. The screen material may be easily removed and other screen material with or without an image installed.

[73] Assignee United States Patent I 72] Inventors Henry J. Bubley Deeriield;

Claude 1'1. Oltra, Chicago, both of 111. [21 Appl. No. 872,957

[22] Filed Oct. 31, 1969 [45] Patented Sept. 28, 1971 American Screen Process Equipment Company Chicago, 111.

Continuation-impart of application Ser. No. 752,023, Aug. 12, 1968.

[54] LOCKING BAR FOR SCREEN-PRINTING FRAME 3 Claims, 7 Drawing Figs.

Primary Examiner-J. Reed Fisher Attorney-Robert E. Wagner ABSTRACT: A screen-printing frame having a screen-tensioning arrangement including a frame supporting a channel member which receives a locking bar. The screen material is positioned over the channel and the locking bar inserted to force the screen into the channel where it is positively gripped. Means is provided to move the channel relative to the frame to provide for tensioning after the screen is securely gripped. The tension on the screen serves to move the locking bar into tighter engagement with the channel, thus increasing the grip on the screen. Resilient means is provided in the bottom of the channel to maintain the screen material in engagement with the locking bar during initial insertion and rotation of the bar to the locked position. The screen material may be easily removed and other screen material with or without an image installed.

PATENIED SEP28 ran SHEET 1 0F 2 HENRY a. auau-zv 2 CLAUDE H. OLTRA INVENTORS ATT'Y.

FIG.

LOCKING BAR FOR SCREEN-PRINTING FRAME This application is a continuation-in-part of our copending application Ser. No. 752,023, filed Aug. 12, 1968.

This invention relates to screen-printing frames in general and, more specifically, is directed to stencil frames particularly adapted for use in screen-printing or the like.

As a preliminary summary, the present invention provides a new and improved apparatus and technique for mounting screen material with or without an image in a frame and thereafter tensioning the same. The novel invention permits it to be removed and replaced easily and assures that the tension of the material will be maintained Tensioning of the screen in the frame is of utmost importance if quality printing is to be obtained. Where the screen is improperly or insufficiently stretched on the frame,

the print registration will vary. Inconsistency in sharpness and quality of the printed surface can and does occur. Uniform release of the screen from the printed surface in off-contact printing is also not obtained and bunching of the screen fabric in front of the squeegee can occur with the resultant smearing or blurring in the print. If the screen is not properly tensioned, rapid screen image deterioration will result. When the screen is properly tensioned, the film or coating applied preparatory to forming the screen-printing plate is more adherent. As used herein, the term screen material is intended to include all woven and nonwoven material such as, but not limited to, nylon polyester, silk, stainless steel and other metals.

In early methods, the screen material was stretched by hand across a wooden frame and stapled or tacked after having fabric was inserted and secured by a cord, rope or elastomeric ring which was wedged into and filled the groove. Installation of the screen material in this form of frame was as follows: The screen material was positioned along one edge and the rope or cord inserted to hold the same. The screen material was then stretched by manual means and the rope or cord forced into the groove, causing the material to stretch slightly more. The tensioning was somewhat better than the earlier techniques, however, as is evident, installation by this method was time consuming and the tension of the screen was not always completely uniform. Obviously, this method left something to be desired from the standpoint of cost and uniformity of tension, particularly in large screens. With the advent of metal mesh screens, neither of the foregoing techniques was satisfactory and other methods were sought."

Mechanical screen-stretching techniques in and of themselves are not completely new, as others attempted to solve the problems presented by the older methods. Several varieties of fabric-stretching devices are pointed out in the publication entitled Screen Process printing, Third Edition, 1964 by Albert Kosloff on pages 16-26.

In one of the mechanical screen-stretching devices, a supporting frame is provided with separate bars to which the screen is fastened and thereafter the floating bars are tensioned by bolts and wing nuts. In a design of this-type, the production or manufacturing cost is increased and the resulting frame does not enclose the printing ink. To obtain adequate strength, the frame size, of necessity, must be increased. Other screen frames utilizing wedges in conjunction with adjustable tensioning means are in use which obviate this specific problem, however, these leave something to be desired from the standpoint of uniform screen tension, acceptability of all screen materials regardless of thickness, manufacturing costs and ease of use. The wedges often slip and are damaged in removal. Also, they require considerable time to install when contrasted with the subject invention. Ex-

emplary of these types are the patents to Lambert (U.S. Pat. No. 2,894,455) and de Groot (U.S. Pat. No. 3,230,872).

The present invention relates to an improved form of frame for tensioning screen plate materials and the like. In the present design, a novel cam locking bar is provided which tightly grips the screen and, during tensioning of the screen, increased its grip on the fabric. Installation and removal of the screen material with or without image is performed quite simply and in a very rapid manner without requiring any special degree of skill. Because of a unique design, any size frame for supporting the tensioning means may be quickly formed, thus contributing to the overall economy. Since the frame may be formed of stable material, it is not susceptible to warp or bowing as experienced in wood screens. It is virtually indestructible in normal use and be economically fabricated by a novel method from extruded stock which can be cut to any desired dimension and joined without any special skill or tooling. Any degree of tension on the fabric may be obtained through a simple adjustment. The supporting frame, besides providing good strength, is extremely lightweight and encloses the entire screen, forming a dam or barrier around the border to confine the ink to areas over the top of the stencil screen. The screen frame can be used and reused, as the locking bar is not susceptible to being damaged during installation and removal. It will accept screen materials of various thicknesses and composition. Because of its unique design, it is economically fabricated.

Other features and advantages will be apparent upon consideration of the objects achieved and an accompanying description of the preferred form of the invention.

It is an object of this invention to provide a printing frame for use in screen-printing having an improved cam locking bar for gripping the screen fabric.

It is a further object of this invention to provide a new and improved frame for screen-printing plates having a rigid outer frame mounting a movable inner frame, the inner frame having a novel cam means thereon to releasably lock screen material to the frame.

It is a further object of this invention to provide a new and improved screen-printing frame having improved constructional features which make it economical to manufacture all sizes from stock which is easily fabricated.

It is a still further object of this invention to provide a new and improved screen-printing frame for tensioning screens which permits the basic parts forming the frame to be manufactured by economical methods such as extrusion and easily joined.

Additional objects will become apparent upon reference to the following description and claims when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a plan view of a screen-printing frame of the present invention;

FIG. 2 is an enlarged cross-sectional view taken generally along line 2-2 of FIG. 1;

FIG. 3 is a fragmentary exploded perspective on a reduced scale of the corner construction of a modified form of screenprinting frame;

FIG. 4 is a top plan view of the corner construction of the screen-printing frame shown in FIG. 3;

FIG. 5 is an enlarged cross-sectional view of the screen printing frame shown in FIG. 3 with the screen material overlying the main frame and inner channel-shaped screen-locking frame and with the locking bar oriented for insertion as taken generally along line 55 of FIG. 4;

FIG. 6 is a plan view of the screen-printing frame shown in FIGS. 3-5 after the cam-locking bar has been inserted; and

FIG. 7 is a cross-sectional view taken generally along line 7-7 of FIG. 6 illustrating the locking bar operatively installed and the screen-locking frame moved to a tensioned position.

Referring now to FIG. 1, a screen-printing frame of the present invention is identified generally by reference character 10. The screen-printing frame consists of outer or main supporting frame elements 11, 12', 13 and 14, each of which is mitered at the corners and joined by any suitable method such as welding, cementing or the like to form a closed polygon. As seen in FIG. 2, the main supporting frame is of general channel shape in cross section, having a bottom web formed integral and supporting upstanding flanges 16 and 17. Frame members 11, 12 and 14 are of similar cross-sectional shape.

Supported on the main frame members are screen fabrictensioning frame members 20, 21, 22 and 23 which are identical in construction and movable relative to the respective associated main supporting frame member. As shown in FIG. 2, the movable screen-tensioning frame member 22 is of general channel construction, having a thickened base portion 24 which supports integral upstanding flanges 25 and 26. The

flanges 25 and 26 cooperate to form an upwardly facing groove indicated generally at 27. The flange 25 is necked in at the upper margin as at 28 while the flange 26 is similarly necked in as at 29, thereby narrowing the mouth or entrance portion to the groove 27 relative to the lower portion of the groove. As noted above, each of the frame locking members be provided with a socket to receive a tool for selective rotation during installation and removal of the screen.

- Each of the respective screen tensioning members 23 receives a cam-locking bar 33, 34, 35 and 36, respectively, in its associated upwardly facing groove. Each of the camlocking bars 33-36 is of identical cross-sectional construction with the length chosen to correspond generally with the length of the corresponding fabric-tensioning frame member. As seen in the cross-sectional view of FIG. 2, the locking bar 35 is of generally arcuate shape in the lower region, with a flat upper surface 36. An integral stop 37 forms a longitudinally continuous handle for rotating the locking bar into position to lock the fabric 38 in the groove. The lower portion of the groove 27 is provided with a resilient means 40 to maintain the fabric 38 in engagement with the arcuate portion of the locking bar during installation of the screen preparatory to tensioning. This function and feature will be described in greater detail after consideration of the modification of FIGS. 3-7.

In FIG. 3, a modified form of screen frame is shown, consisting of rigid frame members 50 and 51 adapted to be joined by a comer plate 52. Each of the frame members 50 and 51 is of identical cross-sectional configuration, consisting of upstanding flange members 53 and 54 joined by a bottom web 55. In spaced relation to the bottom web 55 and disposed in parallelism is a second web 56 which forms a boxlike opening 57, sized to receive the plate 52 with a snug or interference fit. As seen in the cross-sectional view of FIG. 5, the boxlike opening 57 may be provided with spaced ridges 58 and 59 for reasons to become apparent.

In practice, the frame members 50 and 51 are formed by extrusion and then cut to any desired length by'mitering at the adjoining corners. The corner plate 52 and mitered ends are coated with a suitable adhesive such as an epoxy cement and the frame members joined by pushing the corner plate into the position shown in dotted lines in FIG. 4. The raised ridges 58 and 59 in the boxlike opening 57 provide an area for the adhesive to flow to assure rigid corners and a permanent bond. As can be appreciated, with the extruded stock and corner pieces 52 available, any size frames may be made quickly without any special tooling or a high degree of skill.

The movable frame-tensioning channel member shown at 60 in FIG. 5 is functionally identical to the corresponding movable screen-tensioning frame member 22 shown in FIG. 2, having a bottom web 61 supporting upstanding flanges 62 and 63. Resilient means 64 is located in the groove 65 formed by the upstanding flanges 62 and 63 and may be continuous or discontinuous, depending on the fabric. Each of the flanges is necked in as shown at 67 and 68 to provide an opening at the mouth of the groove which is narrower than the balance of the groove. The resilient means 64 may consist of a piece of foam rubber, foam polyurethane or any equivalent which will provide the function to be described below.

A threaded flat-headed bolt 70 is received in a threaded opening in the frame member 60, the bolt being countersunk as at 72 in the outer web 54. The head of the bolt 70 may be provided with a suitable socket opening 75 to receive an Allen wrench. Any equivalent form of socket or tool slot which would permit rotation of the bolt 70 to move the channelshaped member 60 back and forth in the frame 50 is satisfactory also.

The screen material 38 is positioned across the groove 65 and the cam-locking member 36 which is of similar construction to the cam-locking member 35 in FIGS. 1 and 2 rotated to the upright position shown in FIG. 5. In this position, the combined dimension as measured in a horizontal direction from the flat side 77 to the lower arcuate side 78 is less than the minimum dimension across the upper margins of the groove 65 as measured between the necked in surfaces at 67 and 68. This permits the cam-locking bar to be inserted with the handle in a generally vertical position. The screen material 38 is pushed into the groove and into engagement with the resilient means 64. The cam-locking bar 76 is then rotated about 90 to the position shown in FIG. 7 to securely lock the fabric 38 in the groove 65. The resilient means 64 maintains the fabric in engagement with the arcuate surface 78 on the cam-locking bar 76 during the locking movement so that it is tightly gripped by the flanges 62 and 63. The material is further tensioned by rotating the flat-headed screw 70, causing the fabric-locking frame 60 to move outwardly. As the fabric is tensioned, force is applied in a direction which rotates the cam-locking bar 76 counterclockwise, ultimately forcing the stop or handle 80 down against the upper margin of the flange 63 thereby more tightly gripping the screen material 38. The tension on the screen material acts across the arcuate surface, forcing the cam-locking bar upward into tighter engagement with the narrowmouth of the groove and thus increasing the grip on the screen material.

The manner in which the tensioned screen material is held in the frame members 50 and 51 is shown in the fragmentary plan view of FIG. 6. As noted above, the tension serves to lock the cam-locking bar 76 more tightly in the frame member. If desired, the circumferential surface of the locking bar 76 may be roughened or even serrated to improve the grip, however, in actual practice, the smooth surface finish obtained by extruding aluminum has functioned quite well.

The flat-headed screw 70 is chosen of a length so that the inner end engages the inner flange to distribute the tensioning force between both of the flanges 53 and 54. With the screw 70 located at the base of the flanges 53 and 54, even though lightweight aluminum is used, considerable forces can be supported. A polygonal frame of any shape may be provided other than the rectangular frame shown, although rectangular frames are most feasible for present screen-printing equipment.

It is to be appreciated that through reversal of the installation steps, the screen material with or without its design may be easily removed. The threaded members in the frame are backed off to relieve the tension on the screen fabric 38, thereby permitting the locking bar to be rotated to an unlocked position with the handle or stop in a vertical position. Since the stop or handle projects outwardly, a screwdriver or similar tool may be used to pry the handle upward, with the top of the outer flange on the frame functioning as a fulcrum. In practice, this is usually found to be unnecessary, as only slight effort need be exerted to release or unclamp the fabric. The cam-locking bar may then be withdrawn, the fabric removed and new screen material with or without coatings and designs may be readily installed in the manner outlined above.

The tensioning frame of the present invention has found particular application with various types of screen fabrics including nylon and other monofllament synthetics as well as silk and stainless steel mesh. The frame-tensioning member is recessed below the surface of the inner web of the main frame member, thereby avoiding contact with the printing bed. In this manner, the locking member remains protected during use of the frame. This assures cleanliness and a full range of spacing between printing plate and printed part. The tensioning members may be also used to effect slight adjustment of registration of the stencil design after the same is installed in the printing press.

The frame members may be formed from any suitable material with extruded aluminum or plastic being preferred. in the embodiment of FIGS. 3-5 in which the cross section is symmetrical, there is absolutely no waste of stock when the frame corners are mitered at 45. Thus, further savings in fabrication are realized. Also, the screen-tensioning design permits the maximum adjustment in a minimum width of supporting frame, thus reducing the frame bulk. It is envisioned that the frame may also be used to stretch any fabric for flltering and other uses.

We claim:

1. A screen-tensioning arrangement for locking screen material which may be coated or uncoated to a locking frame, said tensioning arrangement comprising a longitudinally extending channel member having upstanding flanges, a longitudinally extending locking bar disposed between said flanges, said locking bar having at least a portion thereof formed with an arcuate surface, said arcuate surface being disposed below the upper margin of said flanges when said locking bar is installed in said channel member between said flanges, the minimum cross-sectional dimension as measured across said arcuate portion being greater than the minimum dimension as measured between said flanges, a portion of said locking bar having a maximum cross-sectional dimension as measured generally perpendicular to a plane incorporating the top surfaces of said flanges when said locking bar is installed, which maximum dimension is lesser than the minimum width of said channel to facilitate insertion of said locking bar into said channel by positioning said portion at an angle to said plane, said screen material being wrapped around said arcuate surface, a portion of said arcuate surface being in opposition to the upper portion of each of said flanges thereby to clamp said screen material between said arcuate portion and said flanges, said screen material, when tensioned, acting to rotate said locking bar relative to said channel member, and means on said locking bar overlying one of said flanges and engageable with a top surface thereon to limit the rotation of said locking bar relative to said channel member.

2. The screen-tensioning arrangement as defined in claim I wherein resilient means is provided in the lower part of said channel member to bias said screen material against said locking bar whereby it will be lockingly gripped between said channel member and locking bar.

3. The screen-tensioning arrangement of claim 1 wherein said means on said locking bar to limit rotation relative to said channel member comprises a continuous handle formed integral with said locking bar and extending along the upper margin of one of said webs to facilitate installation and removal of said screen. 

1. A screen-tensioning arrangement for locking screen material which may be coated or uncoated to a locking frame, said tensioning arrangement comprising a longitudinally extending channel member having upstanding flanges, a longitudInally extending locking bar disposed between said flanges, said locking bar having at least a portion thereof formed with an arcuate surface, said arcuate surface being disposed below the upper margin of said flanges when said locking bar is installed in said channel member between said flanges, the minimum cross-sectional dimension as measured across said arcuate portion being greater than the minimum dimension as measured between said flanges, a portion of said locking bar having a maximum cross-sectional dimension as measured generally perpendicular to a plane incorporating the top surfaces of said flanges when said locking bar is installed, which maximum dimension is lesser than the minimum width of said channel to facilitate insertion of said locking bar into said channel by positioning said portion at an angle to said plane, said screen material being wrapped around said arcuate surface, a portion of said arcuate surface being in opposition to the upper portion of each of said flanges thereby to clamp said screen material between said arcuate portion and said flanges, said screen material, when tensioned, acting to rotate said locking bar relative to said channel member, and means on said locking bar overlying one of said flanges and engageable with a top surface thereon to limit the rotation of said locking bar relative to said channel member.
 2. The screen-tensioning arrangement as defined in claim 1 wherein resilient means is provided in the lower part of said channel member to bias said screen material against said locking bar whereby it will be lockingly gripped between said channel member and locking bar.
 3. The screen-tensioning arrangement of claim 1 wherein said means on said locking bar to limit rotation relative to said channel member comprises a continuous handle formed integral with said locking bar and extending along the upper margin of one of said webs to facilitate installation and removal of said screen. 